310 NERVOUS SYSTEM OF VERTEBRATES. " 



Above the commissures is a slender prolongation of the median 

 ventricle, forward beyond the foramen of Monro, which corresponds 



Fig. 159. — The mesial surface of the right half of the brain of Ornithorhvnchiis. 

 From G. Elliot Smith. 



to the anterior portion of the median ventricle in amphibia (Fig. 



